The term “LIDAR” is a portmanteau of the words “light” and “radar” created to describe systems using light for ranging and depth imaging systems. More recently, the term (LIDAR or “lidar”) forms an acronym for “Light Detection and Ranging.” LIDAR systems form depth measurements and make distance measurements. In LIDAR systems, a source transmits light into a field of view and the light reflects from objects. Sensors receive the reflected light. In some LIDAR systems, a flash of light illuminates an entire scene. In the flash LIDAR systems, arrays of time-gated photodetectors receive reflections from objects illuminated by the light, and the time it takes for the reflections to arrive at various sensors in the array is determined. In an alternative approach, a scan such as a raster scan can illuminate a scene in a continuous scan fashion. A source transmits light or light pulses during the scan. Sensors that can also scan the pattern, or fixed sensors directed towards the field of view, receive reflective pulses from objects illuminated by the light. The light can be a scanned beam or moving spot. Time-of-flight computations can determine the distance from the transmitter to objects in the field of view that reflect the light. The time-of-flight computations can create distance and depth maps. The depth maps are displayed. Light scanning and LIDAR have been used in a variety of applications, including: ranging; metrology; mapping; surveying; navigation; microscopy; spectroscopy; object scanning; and in industrial applications.
Recently LIDAR applications also include security, robotics, industrial automation, and mobile systems. Vehicles use LIDAR navigation and collision avoidance systems. Autonomous vehicles and mobile robots use LIDAR.
In conventional mechanically scanned LIDAR systems, a rotating mirror or mirrors can cause a laser beam to scan the scene in the field of view. Sensors detect light reflected from objects in the field of view by backscattering. The fixed scan patterns result from mechanically rotating a laser or from mechanically rotating a mirror reflecting light from a laser or collimator fed by a laser. These conventional systems include a variety of mechanical components such as motors, rotors, and moving mirrors that have substantial power and weight requirements, require maintenance, and are subject to failure and require repair.
An example LIDAR application is autonomous vehicles. Current commercially available LIDAR systems for autonomous vehicle applications include many components and moving parts. Mechanical motors, rotators, and housing arranged for mounting the system on vehicle roofs are required. U.S. Pat. No. 7,969,558, issued Jun. 28, 2011, entitled “High Definition LIDAR System,” assigned to Velodyne Acoustics, Inc., describes a vehicular system having eight assemblies of eight lasers each to form a sixty-four laser/detector assembly mounted on a vehicle rooftop. The lasers and detectors mount in a rotating housing that rotates at up to 20 Hz. Motors and rotating mechanical parts provide the high-speed rotation. Each of the eight assemblies includes multiple lasers and detectors. Such systems are high in cost, are mechanically and electrically complex, require special power and maintenance, and are physically large and affect the appearance of and the exterior surfaces of the vehicle.